Method and apparatus for coating the edge portions of compressed workpieces



I 3,283,052 E GE PORTIONS E E. MUN R GOA SED w Nov. 1, 1966 METHOD AND APPARATUS F0 TING TH OF COMPRES ORK'PIEC 2 Sheets-Sheet 1 Filed July 16, 1965 I NVEN '3 OR.

A TTOF/YEV Nov. 1, 1966 E. MUNK 3,283,052

METHOD AND APPARATUS COATING THE EDGE PORTIONS o KPIECES F COMPR ED WOR 2 Sheets-Sheet 2 Filed July 16, 1963 I NVEN TOR.

EDMUND MUNK BY V A'TTOANEY United States Patent NIETHOD AND APPARATUS FOR COATING THE EDGE PGRTIONS 0F COMPRESSED WORK- PIECES Edmund Munk, Oberstenfeld, Wuerttemberg, Germany, assignor to Furnierund Sperrholzwerk J. F. Werz, Jr., K.G., Werzalit-Pressholzwerk, Oberstenfeld, Wuerttemberg, Germany Filed July 16, 1963, Ser. No. 295,457 8 Claims. (Cl. 264-248) The present invention relates to a method of bonding a sheet material to one or more lateral wall or surfaces of a compressed material or workpiece in which, due to the fact that this material iscompressed in only one direction upon its opposite outer surfaces, the compressive strength of the inner parts thereof is lower than that of the parts in the vicinity of these outer surfaces. The invention further relates to suitable compression molds for carrying out the new method.

Because of this difference in the compressive strength of the lateral edge portions of such compressed materials or workpieces it has, prior to this invention, been very difficult to secure a coating of sheet material on the surface thereof in such a manner that it would remain intimately connected thereto regardless of the conditions and stresses to which the workpiece might be subsequently subjected. For this reason it has also in the past been impossible to employ the method of bonding a thermoplastic sheet material under heat and pressure to such surfaces since this method requires the base, for example, of chipboard or a similar compressed material, to be sufliciently solid to produce the necessary back pressure so that the liquid plastic of the sheet material can penetrate into the surface of the base and will be intimately and permanently connected thereto when cured and hardened. It has therefore in the past been necessary to resort to different methods of gluing or cementing strips of sheet material to such surfaces. The connection produced by any of these methods has, however, the same disadvantage as that of any glued joint in that there is no direct or positive interlocking engagement between the sheet material and the workpiece and that the glued joint may not last if the workpiece is later exposed to higher temperatures or subjected to considerable mechanical stresses. If the coating should consist of a decorative laminated sheet material which is very expensive, such a material requires a supporting base which, in turn, is glued upon the workpiece. If such a material is used for coating the lateral of a workpiece, it is unavoidable that the brown supporting base will also be visible. Furthermore, it is very difiicult to remove the excess edge portions or burrs of such laminated sheet material. Sheets of polymerized plastic, on the other hand, have the additional disadvantage that they become electrostatically charged and consequently attract dust and dirt. Also the surface finish of such sheet materials is rather soft and easily marred. Finally, sinceat least prior to this inventionthe inner or central parts of the edge portion to be coated had a lower compressive strength than the outer surfaces, the sheet material could not even be glued upon the surface as securely as desired and its adhesion was considerably lower at the areas of a lower compressive strength than at those more highly compressed. Although the present invention may also be applied for considerably improving a glued joint between a sheet material of any kind with the lateral surfaces of a compressed material or workpiece, it is the principal object of the invention to coat these surfaces with a sheet material which consists of or is impregnated with a thermosetting plastic and to carry out the coating process by first applying the sheet material in an only partly condensed condition upon the 3,283,952 Patented Nov. 1, 1966 "ice parts to be coated and by then molding it upon these parts under heat and pressure in a manner so that the originally insufiiciently compressed inner parts of the edge portion will be compressed to a solidity substantially equal to that of the outer parts, and so that the synthetic resin in the sheet material will flow uniformly and combine during its final condensation with the material of the workpiece and the coated edge portions which are finally attained have a smooth non-porous surface of a considerable solidity.

The most important feature of the present inventiona feature which may also be applied in a similar manner in gluing or cementing a sheet material to the lateral surfaces of a workpiece--therefore consists in applying the sheet material under pressure upon the surface by means of a pressure tool which is designed so as to act upon the inner or central parts of the edge portion more strongly than upon the outer parts and thus to compress these inner parts to a solidity and compressive strength substantially equal to those of the outer parts. The same effect may, according to the invention, also be attained by machining the edge portion so that the inner less compressed parts thereof project outwardly and by then applying the sheet material on the surface thereof under such a pressure that these projecting parts are compressed to substantially the same compressive strength as the outer parts. Since the thermosetting sheet material is at the same time heated to the proper temperature, the synthetic resin thereof will melt and penetrate uniformly into the edge portion of the workpiece so that after being cured completely it will permanently lock the coating strip to the surface.

The lateral surfaces of the workpiece which are to be coated do not have to be plane, but they may also be of an uneven, for example, angular shape. The plastic strip is then preferably premolded under heat to the required shape without, however, being finally condensed. The pre-molded strip is then applied upon the uneven or angular surface and molded thereon under heat and pressure in the manner as previously described so that the inner edge portions will at the same time be compressed to a solidity substantially equal to that of the outer parts thereof. In order to exert the pressure in the proper direction upon the uneven edge portion, one or more punches of a shape in accordance with the edge portion may then be pressed in an inclined direction upon the plastic strip.

Another important feature of the new molding method is the simple manner in which the excess parts of the plastic strip which are not secured to the lateral surface of the workpiece may be removed. Since during the molding process these excess parts are heated but not compressed, they are not condensed and therefore become extremely brittle. They may then be removed without difficulty, without leaving any rough edges on the plastic strip, and possibly even without showing any edges. Thus, for example, if the lateral surfaces of a plasticcoated chipboard or the like is coated with plastic strips of the same color or design as that of the plastic sheets on the outer surfaces of the chipboard, the edges of the plastic strips will combine with those of the plastic sheets and will be practically invisible. The finally coated board will then appear to consist entirely of plastic or to be embedded completely in a continuous layer of plastic. This feature constitutes a considerable advantage over the difficult and precarious process of trimming these excess parts off a glued coating strip and of subsequently finishing the edges of this strip by burring, sand papering, or the like. Such glued coating stirps can also never be combined with the outer plastic layers on a chipboard or the like in a manner so that the seams between them will be practically invisible.

The compression mold according to the present invention may be designed for coating the lateral surfaces of only one piece of compressed material or one workpiece or for coating simultaneously in a single operation the surfaces of a plurality of superimposed or laterally adjacent workpieces, for example, of a stack of boards of a compressed fibrous material such as chipboard or the like. According to another feature of the invention, the mold is preferably provided with a plurality of punches or forces which are operated together by a single ram. Each of these punches individually is resiliently mounted by suitable means in or on this ram for separate engagement with one of the superimposed or adjacent workpieces so that minor deviations in size between the different work pieces will be compensated and all workpieces will be equally coated.

According to another feature of the invention,.it is possible to double the number of workpieces which may be coated simultaneou'sily without increasing the height of the compression mold by designing the mold so that the resilient punches are located at the opposite sides of the stack of workpieces and the punches on each side are separated from each other by an abutment of a thickness of one punch and are staggered relative to the resilient punches on the other side of the stack. The resilient punches on each side may then be driven separately from those on the other side by different rams or the abutments on one side with the resilient punches between them and supported thereby may be mounted in a stationary position, while the abutments on the other side with the respective resilient punches between and supported by them are connected to or form a part of the single ram of the machine.

Either of these moulds as above described has the advantage that it permits a lateral surface of a workpiece to be coated only at one side thereof or both lateral surfaces simultaneously at opposite sides of the workpiece. When employing one of the multiple-punch molds, it is thus possible to coat the lateral surfaces of an entire stack of equal workpieces simultaneously either only on one side or on alternate sides or on opposite sides or, if the mold is designed accordingly, even on all four sides.

The operation of coating the lateral surfaces of a plurality of superimposed or adjacent workpieces simultaneously may be carried out very economically by em ploying a single sheet of plastic for coating the corresponding surfaces of the entire stack of workpieces. Since during the molding the parts of the sheet material between the adjacent workpieces are heated but not compressed, they become extremely brittle and may, when the coatings are completely cured, be very easily separated from each other without leaving any rough edges on the inidivdual workpieces.

As previously indicated, the principal object of the invention to compress the inner or central parts of the edge portion of a workpiece to a solidity substantially equal to that of the outer portion may be attained either by first machining this edge portion so that the softer inner parts project outwardly beyond their respective points to which they are to be compressed by one or more heated punches of a shape in accordance with that of the final coated surface and by their compressing these central projecting portions through the plastic strip to substantially the same solidity as that of the outer parts, or it may be attained by making the heated punch or punches of a shape so that their central parts project so as to bulge out the plastic strip and compress the central parts of the edge portion through the plastic strip to the required solidity. In the latter case, the compressing end of the punch or punches may either be solid or it may consist of a flexible material which may be heated, for example, a strip of chrome-nickel steel, and which is connected by means of an intermediate pressure cushion to the actual punch which is likewise adapted to be heated in order to contribute to the heating of the flexible material. Due to the lower solidity of the central parts of the edge portion, the flexible material will under the pressure of the punch be centrally bent and penetrate together with the plastic strip into the softer parts of the edge portion until they have substantially the same compressive strength as the outer portion. At the same time,

' the flexible material will through the plastic strip smooth out and compensate any irregularities on the surface of the edge portion. The flexible material is preferably heated electrically by resistance heating, while the punch itself may be heated in any suitable manner, for example, electrically or by steam.

The various features and advantages of the ,method according to the invention will become further apparent from the following description of the accompanying diagrammatic drawings which also show some of the compression molds or parts thereof, which may be employed for carrying out this method.

In these drawings,

FIGURE 1 is a perspective view shown in longitudinal cross section illustrating the least compressed area of the lateral edge portion formed with a convex surface and of a punch with a plain end surface for molding a strip of sheet material to this surface and for compressing it to a flat shape.

FIGURE 2 shows a longitudinal section of the board according to FIGURE 1, but at the time when through the strip of sheet plastic the convex edge portion of the board is compressed to'a flat shape and this strip is at the same time molded to the board.

FIGURES 3 and 4 show a modificaion of the invention with longitudinal sections of a punch and board in which the positions of the convex and flat edge portions of the punch and board as shown in FIGURES 1 and 2 are reversed. 7

FIGURE 5 shows a longitudinal section of a further moification of the invention, in which the punch is provided with a pressure cushion and a flexible pressure element thereon.

FIGURE 6 shows a longitudinal section .of a further modification of the invention in which three punches similar to the punch according to FIGURES 3 and 4, but resiliently mounted and acted upon by a common ram, are superimposed on each other for simultaneously coating three workpieces.

FIGURE '7 shows a longitudinal section of a further modification of the invention in which two directly adjacent, Vresiliently mounted punches are movable at an inclined angle to a boardtwith a lateral edge portion of an angular cross section for coating this edge portion with a premolded strip of plastic. I

FIGURE 8 shows a longitudinal section of a compression mould for simultaneously coating the opposite edge portions of a larger number of workpieces.

As previously described, it has been found according to the invention that the ditficulty in applying a coating of sheet material uniformly, securely and permanently to a lateral surface of a workpiece which is produced by compression from two opposite sides, for example, a workpiece of chipboard, fiber board, or a similar material, is due to the fact that the compressive strength of the material gradually diminishes toward the center between the outer surfaces upon which the pressure was applied during the production of the workpiece, andthat therefore the compressive strength of the lateral edge portion to be coated also diminishes toward its center.

Therefore, when a coating of sheet material is to be seand may be so low that the central parts of the coating 7 may even separate in the subsequent use of the workpiece, especially as the result of atmospheric influences, changes in temperature or mechanical stresses. Although these facts apply to any method of securing a coating of any sheet material to a lateral surface of such a compressed workpiece, for example, by gluing or cementing, they are especially serious if a sheet of a thermosetting plastic or plastic-impregnated material, for example, melamine-impregnated paper, is to be molded under heat and pressure upon such a surface. If the pressure upon any point of the sheet material is insuflicient, the liquefied synthetic resin thereof will not properly penetrate into the surface to be coated and will not when set lock the sheet material at this point securely to the workpiece. Furthermore, since the proper condensation of the synthetic resin requires the application of a certain amount of pressure and, due to the lack of a suflicient back pressure by the central parts of the edge portion to be coacted, this pressure cannot be exerted, the plastic at these points may under the high temperatures applied burn up and become so brittle that they may easily break under an impact.

The greatness of the present invention resides primarily in the simplicity in which it has solved these difliculties. In order to make the lateral edge portions of a compressed workpiece of a substantially uniform compressive strength so that, when a coating of an only partly condensed sheet plastic or plastic-impregnated material is applied thereon, the present invention provides two methods the effects of which are identical. According to the first of these methods, as illustrated particularly in FIGURES l and 2, the workpiece for example, a plate 1 of chipboard, which is to be coated along at least one of its lateral edge portions, is produced by compression upon its main outer surfaces 2 which during this compression may likewise be coated with plastic. Due to this compression, plate 1 contains outer areas 3 of a higher compressive strength and more central inner areas 4 of a lower compressive strength. In order to provide the lateral edge portion 5 of plate 1 with a substantially uniform compressive strength, this edge portion is first made of a convex shape. The extent of its convexity depends upon the difference between the highest and lowest compressive strength of the areas 3 and 4. This plate 1 is plated in a fixed position on a spacing bar 6 in a compression mold which is only indicated diagrammatically and comprises a punch or force 7 which is adapted to be heated, for example, by steam, and to be reciproacted in the direction of the arrow. Between the convex edge portion 5 and the flat end surface 8 of punch 7 a strip 9 of a partly condensed thermoplastic sheet material is placed which is then pressed by the heated punch 7 against the edge portion 5 until the convexity of the latter is flattened out completely and the entire surface of the edge portion as indicated by the shaded area 10 in FIGURE 2, is compressed to a substantially uniform solidity. The plastic strip as shown at 11 in FIGURE 2 is thereby molded uniformly and intimately to the outer surface of the edge portion, except the free outer edges 12 of the plastic strip which for the lack of pressure thereon become so extremely brittle that they may be broken olf flush with the outer surface 2. If these surfaces 2 also consist of a coating of plastic, the outer edges of the plastic coating 11 on the lateral surface of plate 1 will combine with the coating 2 so that practically no intermediate seam will be visible.

The modification of the invention as shown in FIG- URES 3 and 4 differs from the embodiment according to FIGURES 1 and 2 merely by the fact that the convex edge portion for increasing the compressive strength of the more central parts 14 of plate 13 to substantially the same strength as the outer parts 15 is provided on the end 16 of punch 17, while the lateral edge portion 18 of plate 13 has a plane surface. FIGURE 4 shows that the convex pressure surface 16 on punch 17 presses the strip of plastic 19 against the plane surface 18 of plate 13, as shown in FIGURE 3, and thereby compresses this 6 surface to a concave shape, as indicated at 2th, and to a substantially uniform compressive strength, as indicated by the shaded area 21.

FIGURE 5 illustrates a further modification of the invention. The lateral edge portion of plate 22 has again a plane surface 23 as the plate 13 in FIGURE 3. In order to compress this surface 23 to a concave shape as indicated by dotted lines at 24 and thus the entire surface of the edge portion to a substantially uniform compressive strength, and simultaneously to mold the strip of plastic 25 thereon, the punch 26 which is movable in the direction of the arrow is provided with a pressure cushion 27 and on this pressure cushion with a flexible strip 28, for example, of chrome-nickel steel, which is heated electrically by resistance-heating. Since the heat capacity of this flexible strip is relatively small, punch 26 is additionally heated, as indicated at 29, either electrically or by steam. When punch 26 is moved toward the lateral edge portion of plate 22 and the flexible strip 28 presses the strip of plastic 25 against the plane surface 23, the flexible strip 28 is bent to an arcuate shape, as indicated in dotted lines at 30, since the upper and lower parts of the pressure cushion 27 yield under the back pressure which is exerted by the highly compressed upper and lower edge portions of plate 22 through the plastic strip 25 against the flexible strip 28, while at the same time the relatively soft central part of the surface 23 is pressed inwardly together with the plastic strip 25 until they have a concave shape, as indicated at 24, when the entire surface of the lateral edge portion has a substantially uniform compressive strength and the plastic strip is tightly molded thereon.

FIGURE 6 illustrates diagrammatically a pressure mold which is provided with three superimposed heated punches 31 similar to punch 17 as shown in FIGURES 3 and 4 and provided with convex end surfaces 32 for simultaneously compressing the lateral edge portion 33 of three plates 34 to -a substantially uniform compressive strength in a similar manner as described with reference to FIGURE 4. The three punches 31 are moved simultaneously by a common ram 35 through individual springs 36 or similar cushion means which are provided in order to compensate for minor differences in the sizes of the plates 34. In order to place the plates 34 at the proper level relative to the punches 31, they are mounted on and separated from each other by spacing bars 37. For simultaneously coating the lateral edge portions 33 of all three plates 34 While they are being compressed by the punches 31, only a single sheet 38 of plastic or plastic-impregnated material is re quired. Due to the lack of pressure upon the free portions of the plastic sheet 38 intermediate the edge portions 33 of plates 34, these portions become extremely brittle and may be easily broken off flush with the upper and lower surfaces of plates 34.

FIGURE 7 illustrates diagrammatically a pressure mold for molding a preformed angular plastic strip 40 upon the angular lateral edge portion 41 of a plate 42 which is supported on a spacing bar 43 and the outer surfaces of which may again, as in all embodiments of the invention, be coated with sheets of plastic 44. The edge surfaces of the softer inner parts of this edge portion 41 are precut so as to project beyond the planes 45, as indicated in dotted lines, to which they are to be compressed in order to make the surfaces of the entire angular edge portion of a substantially uniform compressive strength. In order to attain the proper compression of the angular edge portion 41 to its final position 45, it is necessary to exert the pressure thereon at a downwardly inclined direction as indicated by the arrow 46. Since the different surfaces of the edge portion 41 may deviate slightly from their intended sizes and positions, it is advisable to provide at least two separate heated punches 47 and 48 which are mounted in and driven by a common ram 49 in the direction 46 and are individually supported by springs 50 and 51 or other suitable cushion means. The functions of the same as those previously described with reference to FIG-.

URES 1 to 6.

FIGURE 8 finally illustrates the method according to.

the invention for simultaneously coating the opposite lateral edge portions 55 of an entire stack of equal workpieces 56 and 57 which are mounted on and separated from each other by spacing bars 58. The compression mold essentially consists of a stationary part 59 with two heated abutments 60 secured to or integral with the stationary part 56 and facing the left edge portions 55 of workpieces 56,:and three heated punches 61 which are resiliently mounted on springs 62 or similar cushion means in the stationary part 56 and on or between the abutments 60 and are facing the left edge portions 55 of workpieces 57. At the right side of workpieces 56 and 57 a ram 63 is slidable along the horizontal base of the stationary part 56 in the direction of arrow 64. Ram 63 has three heated abutments 65 secured thereto or integral therewith which are disposed at the same levels as the punches 61 and face the right edge portions 55 of Workpiece 57, and it also carries two heated punches 66 which are slidable between the abut-ments 65 and are resiliently mounted on springs 67 or similar cushion means. These punches 66 are disposed at the same levels as the abutments 60 and face the right edge portions 55 of workpieces 56. For compressing the edge portions 55-of all workpieces 56 and 57 to a substantially uniform compressive strength, these edge portions are at first made of a convex shape similarly as the edge portion in FIGURE 1. Punches 61 and 66 are acted upon by springs 62 and 67 respectively, for the same reason as described with reference to FIGURES 6 and 7, namely, for compensating for minor deviations in the length or width of workpieces 56 and 57. The abutments 65 and punches 66 which are driven by ram 63 are staggered relative to abutments 60 and punches 61 for the sole purpose of accommodating the large-size springs 62 and 67 and of reducing the total height of the compression mold. If these springs or other cushion means are made of a size so as not to interfere with each other, a similar arrangement may be employed as shown in FIGURE 6, and all of the punches 61 and 66 may be resiliently mounted on ram 63 at one side of the stationary part 59 of the mold while all of the abutments 60 and 65 may form one solid element with a single plane end surface at the opposite side of ram 63 and secured to or integral with the stationary part 5 of the mold. Similarly as described with reference -to FIG- URE 6, the-re is only a single sheet 68 of plastic or plasticimpregnated material required for coating the edge portions 55 on each side of all of the workpieces 56 and 57. By designing the compression mold accordingly, it Would even be possible to compress and coat simultaneously the edge portions 55 at all four sides of the entire stack of workpieces. Of course, the compression mold and the number of punches therein may also be enlarged to permit an even larger stack of workpieces to be compressed and coated simultaneously. Also, in all of the embodiments of the invention, the molds may be designed so that the workpieces may be worked upon in an upright position rather than in a prone position as illustrated, and those according to FIGURES 6 and -8 may be standing side-by-side instead of lying above each other.

Having thus fully disclosed my invention, what I claim 1. A method of uniformly bonding sheet material with a resin to the lateral surface of a compressed workpiece wherein the inner parts of said workpiece have a lower compressive strength than the outer parts thereof, comprising the steps of: forming a convex surface on the lateral edge portion of said compressed workpiece; placing said sheet material adjacent said convex surface; compressing said sheet material onto said convex surface on said lateral edge portion with heat and pressure to form a flat 8 surface on said lateral edge portion to provide said lateral edge portion with substantially the same compressive strength as said outer parts and to uniformly migrate said resin into said lateral edge portion of said workpiece and bond uniformly said sheet material to the surface of'said lateral edge portion.

2. The method as set forth in claim 1 wherein said sheet material is simultaneously bonded to the surface of the lateral edge portions of a plurality of superimposed workpieces.

3. A method of uniformly bonding sheet material with a resin to the lateral surface of a compressed workpiece wherein the inner parts of said workpiece have a lower compressive strength than the outer parts thereof, comprising the steps of: forming a fiat surface on the lateral edge, portion of said compressed workpiece; placing said sheet material adjacent said flat surface; compressing said sheet material onto said fiat surface on the lateral edge portion with heat and pressure to form a concave surface on said lateral edge portion to provide said lateral edge portion with substantially the same compressive strength as said outer parts and to uniform-1y migrate said resin into said lateral edge portion of said workpiece and uniformly bond said sheet material to the surface of said lateral edge portion.

4. The method as set forth in claim 3 wherein said sheet .material is simultaneously bonded to a plurality of superso that due to the lower compressive strength of said inner parts thereof said tool is bent so as to project with said sheet material essentially into the inner parts of said lateral edge portion to form a concave surface on said lateral edge portion to provide said lateral edge portion with substantially the same compressive strength as said outer pants and to uniformly migrate said, resin into said lateral edge.

portion of said workpiece and uniformly bond said sheet material to the surface of said lateral edge portion.

6. A compression mold comprising at least one pressure element movable toward the surface of a lateral edge portion of a workpiece; a cushion member on said pressure element; a flexible pressure member on said cushion member adapted to bend under the pressure of said pressure element through said cushion member in accordance with pa-rts'of different compressive strength of said lateral edge portion of said workpiece being engaged by said flexible pressure member so as to provide said lateral edge portion with a substantially uniform compressive strength.

7. A compression mold comprising a plurality of pres,

sure elements movable toward the surface of a lateral edge portion of a workpiece; a common pressure element acting simultaneously upon said plurality of said pressure elements and separate resilient means interposed between said common pressure element in each of said plurality of pressure members for compressing the lateral edge portion of said workpiece to a substantially uniform'oompressive strength.

8. A compression mold adapted to receive a plurality of equal workpieces adjacent to each other for simultaneously compressing the lateral edge portions on at least two sides of each of said workpieces to a substantially uniform compressive strength of all said edge portions on said opposite sides; comprising, a plurality of movable pressure members each associated with one of said workpieces and all adapted to engage simultaneously with the lateral edge portions of all of said workpieces at the first of said opposite sides for compressing said lateral edge portions; a

9 10 common pressure element adapted to act simultaneously 2,184,971 12/1939 Allen 156-267 X upon all of said pressure members; separate resilient means 2,550,455 4/ 1951 Davies 16-1 44 interposed between said common pressure element in each 2 729 010 1 195 Markus et 1 15 2 7 of said plurality of pressure members for compensating 2 804 419 8/1957 De Woskin et a1 for minor diiferences in the sizes of said equal workpieces; 5 2831:527 4/1958 Myers et a1.

and a stationary abutment adapted toengage with the lateral edge portions of all said workpieces at the second of said opposite sides for simultaneously compressing said FOREIGN PATENTS lateral edge portions at said second side. 4 1 125 10 1925 Germany References Cited by the Examiner UNITED STATES PATENTS 1,790,178 1/ 1931 Sutherland 161-44 CLIFTON B. COSBY, Examiner.

EARL M. BERGERT, Primary Examiner. 

1. A METHOD OF UNIFORMLY BONDING SHEET MATERIAL WITH A RESIN TO THE LATERAL SURFACE OF A COMPRESSED WORKPIECE WHEREIN THE INNER PARTS OF SAID WORKPIECE HAVE A LOWER COMPRESSIVE STRENGTH THAN THE OUTER PARTS THEREOF, COMPRISING THE STEPS OF: FORMING A CONVEX SURFACE ON THE LATERAL EDGE PORTION OF SAID COMPRESED WORKPIECE; PLACING SAID SHEET MATERIAL ADJACENT SAID CONVEX SURFACE; COMPRESSING SAID SHEET MATERIAL ONTO SAID CONVEX SURFCE ON SAID LATERAL EDGE PORTION WITH HEAT AND PRESSURE TO FORM A FLAT SURFACE ON SAID LATERAL EDGE PORTION TO PROVIDE SAID LATERAL EDGE PORTION WITH SUBSTANTIALLY THE SAME COMPRESSIVE STRENGTH AS SAID OUTER PARTS AND TO UNIFORMLY MIGRATE SAID RESIN INTO SAID LATERAL EDGE PORTION OF AID WORKPIECE AND BOND UNIFORMLY SAID SHEET MATERIAL TO THE SURFACE OF SAID LATERAL EDGE PORTION. 